/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.convert.support;

import org.springframework.core.CollectionFactory;
import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;

import java.util.Collection;
import java.util.Collections;
import java.util.Set;

/**
 * Converts a comma-delimited String to a Collection.
 * If the target collection element type is declared, only matches if
 * {@code String.class} can be converted to it.
 *
 * @author Keith Donald
 * @author Juergen Hoeller
 * @since 3.0
 */
final class StringToCollectionConverter implements ConditionalGenericConverter
{

    private final ConversionService conversionService;


    public StringToCollectionConverter(ConversionService conversionService)
    {
        this.conversionService = conversionService;
    }


    @Override
    public Set<ConvertiblePair> getConvertibleTypes()
    {
        return Collections.singleton(new ConvertiblePair(String.class, Collection.class));
    }

    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType)
    {
        return (targetType.getElementTypeDescriptor() == null || this.conversionService.canConvert(sourceType, targetType.getElementTypeDescriptor()));
    }

    @Override
    @Nullable
    public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType)
    {
        if (source == null)
        {
            return null;
        }
        String string = (String) source;

        String[]       fields      = StringUtils.commaDelimitedListToStringArray(string);
        TypeDescriptor elementDesc = targetType.getElementTypeDescriptor();
        Collection<Object> target = CollectionFactory.createCollection(targetType.getType(), (elementDesc != null ? elementDesc.getType() : null),
                fields.length);

        if (elementDesc == null)
        {
            for (String field : fields)
            {
                target.add(field.trim());
            }
        }
        else
        {
            for (String field : fields)
            {
                Object targetElement = this.conversionService.convert(field.trim(), sourceType, elementDesc);
                target.add(targetElement);
            }
        }
        return target;
    }

}
